[PATCH] mm/vmalloc: allow mem_dump_obj() to be called in interrupt context

[Zhen Lei <thunder.leizhen@huawei.com>]

The function mem_dump_obj() can sometimes provide valuable debugging
information, but it cannot be called in an interrupt context because
spinlock vmap_area_lock has not been protected against IRQs. If the
current task has held the lock before hard/soft interrupt handler calls
mem_dump_obj(), simply abandoning the dump operation can avoid deadlock.
That is, no deadlock occurs in extreme cases, and dump succeeds in most
cases.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 mm/vmalloc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ccaa461998f3c37..cdd36c5a1aa16f8 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4034,6 +4034,9 @@ bool vmalloc_dump_obj(void *object)
 	struct vm_struct *vm;
 	void *objp = (void *)PAGE_ALIGN((unsigned long)object);
 
+	if (unlikely(spin_is_locked(&vmap_area_lock)))
+		return false;
+
 	vm = find_vm_area(objp);
 	if (!vm)
 		return false;
-- 
2.25.1